The undersea lair of a giant worm that ambushed sea creatures 20 million years ago was discovered by fossil hunters in Taiwan.
The researchers believe that the 2-meter-long den found in ancient marine sediments housed a prehistoric predator that erupted from the seabed and dragged unsuspecting animals into its lair.
The creature may have been similar to today’s ferocious “Bobbit worms”, which lurk in burrows of sand at the bottom of the sea, with antennae projecting to detect passersby. Although soft-bodied, the worms have sharp and powerful jaws that can cut a fish in two.
“After 20 million years, it is not possible to say whether this was done by an ancestor of the Bobbit worm or another predatory worm that functioned in more or less the same way,” said Professor Ludvig Löwemark, a sedimentologist at National Taiwan University. “There is a great variation in the behavior of the Bobbit worm, but it looks very similar to the shallow worms that reach out, grab fish and pull them down.”
Bobbit worms, or Eunice aphroditois, Take their names from the John and Lorena Bobbitt case, in which the latter – after years of physical and sexual abuse – cut off the former’s penis with a kitchen knife.
Löwemark and his colleagues discovered the fossilized lair and the like while studying 20 million-year-old sedimentary rocks on the northeast coast of Taiwan. Burrows are reinforced with mucus and are more resistant to weathering, which means that they sometimes protrude from the rocky faces of fine sandstone.
Scientists were initially baffled by the remains of fossils, but gradually converged on a likely suspect. At the top of the 3 cm wide burrows, they noticed a distinct pattern that looked like several inverted funnels stacked on top of each other. This gave the opening of the lair a feathery appearance in the cross section.
Having discarded other digging creatures, such as shrimp, and marks left by stingrays hitting the seabed with water jets to expose the shrunken prey, the researchers concluded that the feathered entrance to the burrow was caused by a worm-like hunting strategy Bobbit.
When the worms pull their prey into their lair, the top of the den collapses and the worms have to rebuild it before ambushing their next meal. “This results in the pile of cone-in-cone structures that form the ‘feathers’ around the top of the tube,” said Löwemark.
Writing in Scientific Reports, the researchers describe 319 of these shallow water holes preserved in 20-m-old sandstone at Geopark Yehliu and the Badouzi headland, suggesting that the local seabed was colonized by animals. The traces of fossil traces, called Pennichnus formosae, they are vertical on the top meter and then horizontally for about a meter, perhaps because deeper sediments are more difficult to bury and the water is less oxygenated. Bobbit worms breathe by absorbing oxygen through the skin.
The researchers expected the burrows to contain fossilized remains of prey or worms themselves, but have found none so far. One reason, Löwemark said, is that digging worms usually inject their feces into the water and let it go, scattering bone fragments from previous meals everywhere.
Löwemark dreams of studying Bobbit worms in the wild one day. “They are impressive animals,” he said. “You don’t necessarily want to dive too close if you find one.”